³He spin filters for spherical neutron polarimetry at the hot neutrons single crystal diffractometer POLI-HEiDi

Abstract

3D vector polarisation analysis called also SNP (Spherical Neutron Polarimetry) is a powerful method for the detailed investigation of complex magnetic structures. The precise control of the incoming and scattered neutron polarisations is essential for this technique. Here we show an instrumental setup, that was recently implemented on the new single crystal diffractometer POLI-HEiDi at the FRM II for performing SNP experiments using two 3He spin filters for the production and for the analysis of the neutron polarisation. The design and optimisation procedure for the used spin filter cells are presented. Methods for in-situ measurements of the incoming polarisation as well as the particularities of the using two spin filters and corrections for the time dependent relaxation are discussed. Statistical precision of 1% has been achieved for the measurements of the polarisation matrix under the real experimental conditions using described cells and applying proposed correction method for the data.